AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Chlorine Activation and Speciation during Nocturnal Processing of Authentic Biomass Burning Aerosol
LYDIA JAHL, Lexie Goldberger, Adam Ahern, Joel A. Thornton, Ryan Sullivan, Carnegie Mellon University
Abstract Number: 502 Working Group: Aerosol Chemistry
Abstract Nitryl chloride (ClNO2) is a nighttime reservoir of NOx that is formed from the uptake of dinitrogen pentoxide (N2O5) into particles containing chloride. ClNO2 was thought to be formed only in the presence of chloride from sea spray aerosol, but its recent detection in areas far from the ocean has raised the possibility that other unrecognized particulate chloride sources make important contributions to chlorine activation chemistry. ClNO2 is photolyzed each morning to produce the chlorine radical and recycle NOx, thereby increasing the atmospheric oxidant budget. The formation of ClNO2 from the heterogeneous reactions of N2O5(g) with authentic biomass burning aerosol has not previously been studied. We observed the rapid production of N2O5 and then ClNO2 from a variety of fuels using a smog chamber at Carnegie Mellon University. Iodide adduct chemical ionization mass spectrometry was used to measure gas phase ClNO2 and N2O5 and acetate chemical ionization mass spectrometry was used to measure gaseous HCl and other compounds, while a soot particle aerosol mass spectrometer measured changes in aerosol composition. Upon the addition of ozone to biomass burning smoke, N2O5 was consistently rapidly formed and ClNO2 was subsequently detected in the gas phase. During experiments at high relative humidity, we observed decreases in particulate chloride and increases in particulate nitrate which we believe are due to acid displacement of HCl(g) by HNO3 since no additional ClNO2 was produced in the gas phase. The reactive uptake probability of N2O5 on authentic biomass burning aerosol and the yield of ClNO2 were determined for the first time using smog chamber experiments on smoke from biomass fuels including sawgrass, palmetto leaves, and ponderosa pine. These experiments confirm the formation of N2O5 and ClNO2 in biomass burning emissions and suggest that biomass burning is a likely source of continental ClNO2.